Broadband wireless communications enable a user to enjoy numerous wireless mobile services such as those of high-speed data downloading, online shopping, mobile video chatting and mobile TV, and therefore represent the dominating development tendency in the future mobile communications. If the future broadband wireless communication system always employs the traditional single-carrier transmission approach, InterSymbol Interference (ISI) of a broadband wireless communication signal would increase significantly.
To eliminate the inter-symbol interference of a broadband wireless communication signal, an OFDM technology is proposed to improve the performance of demodulated signals and adopted and standardized in both the Long Term Evolution (LTE) project of the 3GPP and the 802.16 architecture of the IEEE. The OFDM is also known as a fundamental technology in the future broadband wireless mobile communication system. In the case of the OFDM modulation approach, physical resources are divided based on the number of sub-carriers in the frequency domain and the number of OFDM symbols in the time domain, a basic Physical Resource Block (PRB) includes a predefined combination of several sub-carriers and several OFDM symbols, and each user or channel is allocated with one or more basic Physical Resource Block for the communication and transmission of a wireless signal, as shown in FIG. 1, in which 9 PRBs are allocated to 6 users, with each PRB being a basic unit of mapping transmission data into the physical layer.
The structure of each of the PRBs may be illustrated with a 2-dimension structure in the time and frequency domains as shown in FIG. 2, thus the PRB is also referred to as time and frequency resource block unit. As shown, the time and frequency resource block unit includes NT OFDM symbols in the time domain and NF OFDM sub-carriers in the frequency domain, with the total number of symbols in the time and frequency resource block unit being N=NT×NF. The symbols in the time and frequency resource block unit are represented as follows:
      s                  N        T            ×              N        F              =      [                                        s                          0              ,              0                                                            s                          0              ,              1                                                …                                      s                          0              ,                                                N                  F                                -                1                                                                                      s                          1              ,              0                                                            s                          1              ,              1                                                …                                      s                          1              ,                                                N                  F                                -                1                                                                          ⋮                          ⋮                          …                          ⋮                                                  s                                                            N                  T                                -                1                            ,              0                                                            s                                                            N                  T                                -                1                            ,              1                                                …                                      s                                                            N                  T                                -                1                            ,                                                N                  F                                -                1                                                          ]  
All of the symbols in the time and frequency resource block unit can be data symbols. Alternatively, a part of the symbols in the time and frequency resource block unit can be pilot symbols designed for channel estimation of signals received at the receiving side. FIG. 3 is a schematic diagram showing the positions of the pilot symbols and data symbols in the time and frequency resource block unit.
In this case, time and frequency resource block units from multiple users can be transmitted through orthogonal OFDM sub-carriers, with each user occupying a different sub-carrier, so that the division multiplex and multiple access of multiple users is implemented. When the OFDM system is applied to a cellular mobile system and an approach of single frequency networking is used, if users in different cells transmit and receive data via the same sub-carrier, signals transmitted and received by users in adjacent cells interference with each other.
To alleviate the interference between signals of multiple users in multiple cells when the OFDM system employs the approach of single frequency networking, the applicant has proposed Block Repeat (BR) transmission solutions in Chinese Patent Application No. 200710063115.5, including solutions of Block Repeat Division Multiplex (BRDM) and Block Repeat Division Multiple Access (BRDMA). The combinations of such BR transmission solutions with OFDM may be referred to as Block Repeat OFDM (BR-OFDM) and Block Repeat OFDMA (BR-OFDMA), respectively. The Block Repeat transmission solution is implemented through the repeat of the basic time and frequency resource block units, and does not limit the modulation and multiple access approaches at the physical layer. Therefore, the Block Repeat Division Multiple Access solutions can be combined with various basic multiple access approaches to construct various multiple access transmission solutions. For example, the combination of the Block Repeat Division Multiple Access solution with Interleaved FDMA (IFDMA) results in a BR-IFDMA solution, and the combination of the Block Repeat Division Multiple Access solution with DFT-Spread OFDM (DFT-S-OFDM) results in a BR-DFT-S-OFDM solution. Typically, the IFDMA and DFT-S-OFDM may be generally referred to as Single-Carrier FDMA (SC-FDMA), and thus the combination of BRDM with SC-FDMA may be referred to as BR-SC-FDMA.
FIG. 4 shows the structure of BR-OFDM physical resources of a single user. As shown, a Block Unit (BU) is a basic unit for Block Repeat, and one BU is repeated for 6 times in FIG. 4, resulting in BU1, BU2, . . . , BU6, that is, 6 BUs transmit the same data. The times for which a block is repeated is referred to as Repeat Factor (RF), which is 6 in the present example. Each of the repeated BUs is weighted using a weight factor, and a BR weight factor sequence (or referred to as a Repeat Code (RC)) of C0C1 . . . , CRF-1 is provided by the transmitting side. In the BR transmission, BU are weighed, repeated and mapped into designated time and frequency positions.
Generally, however, the RC sequences of BR signals occupying the same time and frequency resources are not orthogonal, or the orthogonality of the received signals is lost due to a channel change although the RC sequences are orthogonal, the orthogonality of different user signals cannot be ensured at the receiver. As a result, there exists Multiple Access Interference and inter-symbol interference between the various user signals after the BR demodulation at the receiver.